1. Field of the Invention
This invention relates generally to trap circuits used for removing interference signals in various signal processing circuits such as a television receiver, video tuner, satellite communication system or the like.
2. Prior Art
Trap circuits of bridge T type used for the above-mentioned various apparatus handling radio frequencies are well known in VHF/UHF/SHF/microwave art. In conventional trap circuits of the above-mentioned type, an inductor of variable inductance type is used so as to obtain a desired frequency, while a variable resistor is used for obtaining maximum attenuation. However, with such a conventional trap circuit the capacitance of a capacitor coupled with the variable inductor in parallel must be extremely small when it is necessary to obtain a very sharp trapping characteristic at a high frequency such as several hundreds MHz, while the resistance of the variable resistor must be very large. As a result, insertion loss of such a trap circuit is very large. When it is intended to obtain a further sharper trapping characteristic, the value of the capacitors must be further reduced to be smaller than 1 pF which is difficult to actualize.
In the case two traps are needed, when the conventional trap circuit is adjusted so that the attenuation of one trap is maximum, then the attenuation of the other trap does not equal maximum.